Glaucoma is a major cause of blindness in the world, and currently affects 2.2 million United States citizens. While conventional treatments to lower intraocular pressure (IOP) can stabilize vision in many patients, others continue to lose vision in spite of apparently good pressure control. This suggests that unique hanges may occur in glaucoma that leave remaining optic nerve fibers increasingly susceptible to IOP. Identifying and understanding such changes will lead to potent new methods of preventing vision loss in glaucoma, particularly if applied to retinal cells before they are committed to cell death. This proposal concentrates on the hypothesis that both elevated IOP and aging impair the ability of retinal ganglion cells (RGC) to support the organization of the axonal cytoskeleton and axonal transport, functions critical to their survival. This will be tested by performing gene array analysis on inner retinal tissue from a rat model (8 months old) of elevated IOP to determine the range of gene responses common to these biological responses. These findings will be confirmed by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and immunohistochemistry will be used to localize protein products to the specific cells of this layer. Identification of gene changes specifically to RGC will be done using laser capture microdissection of RGC labeled by fluorescent tracers and qRT-PCR. Reversibility of these gene changes will then be tested in eyes in which pressure is lowered by cyclodialysis following an initial period of IOP elevation. These will be evaluated in the inner retina by gene array analysis and in RGC specifically with qRT-PCR. Finally, qRT- PCR will be used in tissue from aged animals (28 months old) to evaluate RGC gene responses to elevated IOP and their ability to recover following pressure normalization by cyclodialysis. Relevance to public health: These experiments will provide information on cellular mechanisms of retinal damage and visual loss in glaucoma, a disease expected to increase in the United States by 50% in the next 15 years due to rapid aging of our population. This knowledge will lead to effective new therapies that can be added to conventional pressure-lowering treatment to protect vision in patients at greatest risk of progression, such as the elderly and those with advanced disease.